Wiring boards have been used in various applications, and increasingly demanded to be adaptable to larger electric currents and higher voltages in the cases where they are used in vehicle-mounted applications, along with recent wide spread of electric automobiles and hybrid automobiles. Therefore, for coping with such larger electric currents and higher voltages, conductor patterns as inner-layer patterns need to have larger thicknesses more than, e.g. 100 μm. Gaps between the conductor patterns are filled with a resin in a prepreg material (see PTL 1 and PTL2).